It is well known that a dielectric substrate (e.g., plastic) can be electroplated by first depositing a thin film of metal (e.g., copper) on its surface and then cathodizing the film in an appropriate electroplating bath to deposit the desired metal layer(s) (e.g., copper, nickel, chrome, etc.) atop the film. The metal film may be applied by a variety of techniques including electroless chemical deposition, vapor deposition, sputtering, etc. Polymeric substrates (e.g., acrylonitrile butadiene styrene, phenylene oxide, etc.) are typically so filmed by electrolessly depositing copper or nickel onto a previously etched and catalyzed surface of the substrate. Electroless copper preplating films are the most popular, and can be laid down using any number of a commercially available proprietary processes such as: the Crownplate.TM. system marketed by the Shipley Company; the Macuplex.TM. system marketed by the MacDermid Company; and the Enplate.TM. system marketed by Enthone, Inc. While each of these proprietary systems differ somewhat from the other they nonetheless function in essentially the same way--to wit, the polymer surface is primarily: cleaned; etched (i.e., in chromic acid or chromic-sulfuric acid) to provide micropits on the surface for anchoring the electrodeposit thereto; catalyzed (i.e., with tin/palladium salts or colloids) to initiate and nucleate the chemical deposition of copper from solution; and finally immersed in an electroless copper bath to chemically deposit the copper onto the surface. A variety of rinsing and neutralizing steps are interspersed the aforesaid primary steps as may be required. Alternatively electroless nickel preplating films may be deposited in essentially the same manner as is well known in the art. The substrate is then electroplated as desired by cathodizing the copper or nickel film in an appropriate electroplating bath(s).
Heretofore electroplating selective areas of dielectric substrates typically involved masking-off the substrate to sharply delineate those areas where plating was sought from those areas where plating was unwanted (hereafter the "no-plate" zone). Demasking of the substrate followed plating. Masking and demasking operations are often so cumbersome that many electroplaters will simply plate the entire surface rather than mask and demask the part being plated. Our copending U.S. patent application Ser. No. 520,478, which is filed concurrently herewith and assigned to the assignee of the present invention, describes a process which eliminates the need for masking and demasking operations ffect selective electroplating. According to Ser. No. 520,478 maskless selective plating of a dielectric substrate is effected by: (1) electrolessly depositing a thin film of copper on the surface of the substrate; (2) destroying a narrow band of the film by means of a laser beam so as to expose a narrow strip of the underlying dielectric which electrically isolates one zone of the film from another; (3) immersing the part in an electroplating bath; and (4) therein cathodizing only the zone of the film where plating is sought.
Many commercial products, and particularly automobile trim parts, comprise a dielectric polymeric substrate (e.g., ABS, phenylene oxide, etc.) having a composite surface including a decoratively metal plated (e.g., chromium) portion side-by-side and unplated substantially dielectric portion (i.e., exposed or painted substrate). The unplated portion may either match or contrast (e.g., black) with the principle color of the automobile. If the substrate itself is an acceptable color and/or texture it may serve as part of the composite surface. In such instances the substrate is merely masked off in areas where plating is not desired. Demasking follows. Such masking and demasking operations however are both cumbersome and costly. Where a painted surface is required, some manufacturers simply metal plate a large surface of the substrate and then selectively paint over the metal layer to achieve the desired aesthetic affect. Such plating-painting practices: consume excess electrolytic metal and associated plating current; limit the number of parts than can be plated at any one time; and typically result in relatively poor adhesion between the paint and the underlying electrolytic metal layer.
It is an object of the present invention to provide a time and cost effective process for providing a dielectric substrate with a composite surface including a metal plated portion side-by-side an unrelated substantially dielectric portion without the need for cumbersome masking/demasking operations.
It is another object of the present invention to provide a time and cost effective process for providing a dielectric substrate with a composite metal-paint surface.
It is still another object of the present invention to provide a process for providing a polymeric substrate with a composite surface including strongly adherent metal and paint portions in side-by-side relation one to the other.
These and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.